The objective of the research proposed here is to continue an established program of studies related to the chemistry of human chorionic gonadotropin (hCG) placing new emphasis on these elements of immunochemistry that relate to potential applications in reproductive biology. Included among our goals is a plan to increase knowledge of how to produce antibodies and apply them in assays with greater specificity for hCG, so that there may be improvements in techniques to detect the hormone in different physiological states. We plan to develop antisera to specific regions of the a and b subunits of hCG, so that these reagents may be employed to answer questions about whether these molecules enter target cells. Such antibodies may also be used to detect changes in molecular conformation when the hormone's subunits combine with each other or to map the exposed surface when the hormone is bound to its receptors. We also intend to define better the nature of the molecules, found in the urine of pregnant women, that have immunosuppressive properties. These studies and others that are detailed in the application are directed at the longer term goal of making useful application of recent new information concerning the chemistry of hCG to the solution of problems in reproductive biology.